1. Field of the Invention
The invention relates to fluidized catalytic cracking (FCC) processes and to the composition of the particles circulated in these processes. The invention specifically relates to the use of "metal traps" in FCC catalysts and to the use of sulfur adsorbing or transferring particles to reduce the release of sulfur oxides from FCC units. More specifically the invention relates to the simultaneous use of catalyst components designed to reduce the deleterious effects of vanadium and nickel on FCC catalyst together with spinel-containing sulfur oxide transfer particles.
2. Prior Art
The use of additives to counter the effects of metals such as vanadium and nickel on FCC catalysts and the use of additives to reduce the discharge of sulfur oxides with FCC flue gases are both described in the prior art.
The catalyst deactivating effects of vanadium can be diminished by incorporating a vanadium trapping agent into the catalyst. Alumina and rare earth oxides have been described as such a trapping agent in U.S. Pat. No. 4,988,653 issued to J. A. Herbst et al.
U.S. Pat. No. 4,971,935 issued to R. Bartek et al. is believed relevant for its teaching as to the use of a catalyst component comprising calcium and tin, such as calcium stannate, to reduce the deleterious effects of metals in the feed stream charged to an FCC process.
U.S. Pat. No. 4,451,355 to B. Mitchell et al. discloses various vanadium passivating additives consisting of multimetallic calcium-titanium and calcium-zirconium oxides and various other calcium-containing oxides.
The use of spinel-containing discrete entities circulated with the FCC catalyst to retain sulfur oxides formed in the regeneration zone and to release hydrogen sulfide in the FCC reaction zone is described in U.S. Pat. No. 4,957,892 issued to J. S. Yoo et al.
U.S. Pat. No. 4,341,661 issued to K. Baron et al. is believed relevant for its teaching that a bastnaesite component is effective in reducing the sulfur oxide and carbon monoxide emissions from an FCC regeneration zone. The bastnaesite may be employed in the form of separate particles which circulate through the FCC unit with the catalyst or the bastnaesite may be physically incorporated into the catalyst.
European patent application No. 89306806.4 (EP-A-350280) by L. Upson et al is addressed to the use of an FCC catalyst composition comprising bastnaesite, a zeolite and alumina. The bastnaesite is described as improving the metal tolerance of the catalyst and is not employed as a sulfur oxide transfer agent.
U.S. Pat. No. 5,007,999 issued to A. A. Chin is believed pertinent for its teaching of a process for reducing sulfur oxide emissions from an FCC unit while also addressing the problem of metal contamination of the catalyst. In this process the metals are passivated with a sulfur compound such as hydrogen sulfide or a thiol, with the sulfur reacting with the metal. The sulfur is released in the regeneration zone and converted into sulfur oxides which in turn are removed by contact with metal containing particles. This reference refers to several metal-containing screte entities used for this purpose including alumina, oxides of Group IIA metals such as magnesia and cerium oxides. The reference indicates the use of metal-containing spinels including those containing magnesium is preferred.
U.S. Pat. No. 4,889,615 issued to A. A. Chin et al. is believed to be pertinent for its teaching as to reducing sulfur oxides emissions from an FCC regeneration zone while simultaneously protecting the zeolitic component of the catalyst with a metal trap, with both functions being performed by a single additive comprising a dehydrated magnesium-aluminum hydrotalcite. The reference describes the use of magnesium-aluminate spinels to control sulfur oxide emissions.